The present invention relates to a process for the preparation of 2-hydroxypyridine or quinoline compounds and more particularly 2-hydroxypyridine or quinoline carboxylic acids and esters.
2-Hydroxypyridine or quinoline carboxylic acids and esters are useful as herbicide and pharmaceutical intermediates. One method for their preparation involves oxidizing quinolinic acid to obtain 2 3-bis(methoxycarbonyl)pyridine N-oxide, treating the N-oxide with acetic anhydride to give the 2-acetoxy compound, and hydrolyzing to give 6-hydroxy-2,3-dimethoxycarboxylpyridine in 27.5% overall yield; see E. Spinner et al., J. Chem. Soc. (B), 289 (1971). Another method involves reacting an ester of coumalic acid with ammonia to yield 2-hydroxy-5-pyridinecarboxylic acid; see W. T. Caldwell et al. J. Am. Chem. Soc. 66, 1479 (1944). Another method involves converting alpha-pyrone-6-carboxylic acid with ammonium acetate and glacial acetic acid into 2-pyridine-6-carboxylic acid; see J. Fried et al., J. Org. Chem. 6, 566 (1941).
Unsubstituted 2-hydroxypyridines may be prepared in several ways. T. Umemoto et al., Tetrahedron Letters 28(24), 2705 (1987) teach reacting N-fluoropyridinium triflate with alkaline solution to give 50% 2-hydroxypyridine. Research Disclosure 24016 (1984) teaches contacting a 3,4-dihydro-2-pyridone with a catalytic amount of a Group VIII metal on a support in a suitable solvent at elevated temperatures to produce 2-pyridinols. Another method consists of a 3-step sequence involving oxidation of a pyridine compound with a peracid to give a pyridine-N-oxide, followed by treatment of the N-oxide with PCl.sub.5 to give the corresponding 2-chloropyridine, and finally hydrolysis to the pyridinol. See H. L. Bradlow et al., J. Org. Chem. 14 509 (1949).
N-Oxides of 2-pyridine carboxylic acids react with tertiary amines and acetic anhydride in the presence of halogen-producing compounds to yield 2-halopyridine carboxylic acids as taught by U.S. Pat. No. 4,556,716 and in the presence of nitriles to yield 2-aminopyridine carboxylic acids as taught by U.S. Pat. No. 4,496,733. U.S. Pat. No. 4,797,149 teaches compounds such as ethyl 2,6-bis(trifluoromethyl)-4-hydroxy-3-pyridinecarboxylate. U.S. Pat. No. 4,801,716 teaches a process for the preparation of heptachloropicoline.
U.S. Pat. No. 4,797,409 teaches 1-hydroxy-2-pyridones which are prepared by reacting 6-halogenomethyl-2-pyrones with phenols and then converting the intermediate by reacting with hydroxylamine.
Elemental fluorine is a well known fluorinating agent but it has rarely been used as an oxidant to prepare nonfluorinated organic compounds; for examples, see N. Watanabe et al., Bull. Chem. Soc. Jpn. 54, 127 (1981) which teaches oxidizing alcohol to aldehyde with carbon impregnated with elemental fluorine and S. Rozen et al.. Angew Chem. Int. Ed. Engl. 25(6), 554 (1986) which teaches treating olefins in aqueous acetonitrile with elemental fluorine to give epoxides.
According to S. Rozen et al., J. Am Chem. Soc. 109, 3789 (1987) and S. Rozen et al., J. Org. Chem. 53, 1123 (1988), acetyl hypofluorite, which is a useful fluorinating agent, oxidizes pyridine to yield 2-acetoxypyridine. The article reports that an electron-withdrawing group at the 2-position inhibits the reaction
Pyridine esters when treated with elemental fluorine in organic solvent yield the corresponding 2-fluoropyridines according to M. Van Der Puy, Tetrahedron Letters 28(3), 255 (1987) and U.S. Pat. No. 4,786,733.
Because they are useful as herbicide and pharmaceutical intermediates, a simple one-step process for the preparation of 2-hydroxypyridine or quinoline carboxylic acids and esters in high yield is needed.